Conventionally, as a representation method of an image in, for example, a poster and a Web page used for an advertisement, a notice of an event, and the like, a method is known in which a plurality of images to be combined (hereinafter referred to as “material images”) are arranged like tiles and the images are represented as a mosaic image (for example, a mosaic art and a photo mosaic). In this representation method, for example, an image (hereinafter referred to as an “original image”) to be an original of a picture of the mosaic image is divided into a plurality of regions. Each material image is assigned to, for example, a region whose color tone, pattern or the like is similar to those of the material image. Thereby, a mosaic image which represents a picture of the original image is generated.
On the other hand, a technique is known in which a server device acquires images, which are provided from a user as material images, from a terminal device through a network and causes the terminal device to display a mosaic image generated by using the acquired images. In this case, what images are the material images depends on a determination of the user who provides the images. Therefore, when such images are used as the material images, a problem to be solved is how to generate a mosaic image which has high recognizability of a picture of the original image.
For example, Patent Literature 1 discloses a technique, the object of which is to provide a mosaic image that has high recognizability. Specifically, when a mosaic image providing device determines a block, in which a material image posted by a user is placed, from a plurality of blocks obtained by dividing a target image which is an original of the mosaic image, the mosaic image providing device determines a block selected by the user to be a block in which the material image is placed or automatically determines a block in which the material image is placed without being limited by an image of the block. Further, the mosaic image providing device corrects color of a material image so that an average density value of a basic color of the material image is an average density value of the basic color of a block in which the material image is placed. Furthermore, until when the number of material images posted by the user reaches a number necessary to complete the mosaic image, a mosaic image in which the material images are placed in only a part of the blocks is displayed on the terminal device. In other words, a mosaic image in an uncompleted state is displayed.